Exploring the characteristics of coke formation on biochar-based catalysts during the biomass pyrolysis

Catalyst deactivation by coke formation is one of the main barriers to the application of biomass catalyst pyrolysis. The coke characteristics of biochar-based catalysts (BZ) were systematically studied at different reaction times and temperatures in a tube furnace reactor with poplar wood chips as the biomass feedstock. The morphology, pore structure, chemical structures and composition of soluble coke of BZ were investigated separately. And the reaction mechanism of coke formation was established. Coke was formed by the continuous dehydrogenation and deoxygenation of small molecule reactants and the aggregation. And at low temperatures, coke tended to be generated on the outer surface, but at high temperatures, coke was preferentially formed in the catalyst pore channels. Phenols and oxygenates were the main substances that promoted the coke formation. The high temperature and long reaction time promoted the conversion of coke formation from aliphatic hydrogenation to aromatization and graphitization. The concept of “coke level” based on hydrogen pool theory can better measure the amount and the degree of graphitization of coke. The greater the Clevel, the higher the graphitization and the more the amount of coke. This study is helpful to understand the coke nature and formation mechanism on biochar-based catalysts, which is beneficial to the application of biochar-based catalysts in the biomass pyrolysis.